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Can community diversity predict predator abundance?

Riparian habitats, which include streams and the surrounding land, are sites of material and energy exchange between land and water. Predators that use these areas, such as river otter and mink, rely on both systems for cover and prey (i.e., fish, crayfish, muskrat).

Unusually cold winter temperatures in southern Illinois created this beautiful scene, revealing just how many animals use frozen streams for travel.

High-quality riparian habitats are likely more attractive to predators because their prey is more abundant in high-quality sites. However, predators can affect the prey community themselves, potentially increasing ecosystem biodiversity and thus affecting measurements of site quality. Before determining how this relationship works we first must ask, does a relationship between habitat quality (measured by community diversity) and predator site use occur across stream-terrestrial system boundaries?

Field assistant surveying for tracks on a snowy bank.

We sampled 77 stream sites in Illinois, USA multiple times over a 3 year period for river otter and mink using signs left behind by individuals (tracks and scat) to establish recent site use. We then used multi-season occupancy modelling to determine if stream quality predicted predator site use over time. Stream quality was represented by stream community data, including fish, mussels, and other macroinvertebrates, collected by the state of Illinois.

River otter track in the sand along stream bank in Illinois, USA.

We primarily identified species as having used the site based on finding tracks along the stream bank. As expected, the amount of mud, sand, soft snow on the bank affected our ability to find river otter and mink tracks. River otter used and remained in sites with a high number of fish species. Additionally, they moved into sites with increased macroinvertebrate community diversity (i.e., macroinvertebrate index of biotic integrity) and when beaver used the site previously. Mink were more likely to use a site when muskrat were previously found and, similarly to river otter, if the site had high numbers of fish species. An index of the mussel community positively predicted mink continuing to use a site over time.

Not all of our surveys were on streams with wooded riparian buffers after a recent snow! Most of our surveys were conducted along muddy stream banks. Some, like this one, were completely surrounded by agricultural fields.

Taken together, our results show habitat use by mink and river otter were predicted by aspects of prey diversity and presence, as well as diversity of lower trophic levels (e.g., macroinvertebrates), indicating the importance of stream and riparian community com­position for riparian predators.

Oikos Journal

Oikos is a journal issued by the Nordic Ecological Society and is one of the leading peer-reviewed journals in ecology. Oikos publishes original and innovative research on all aspects of ecology, defined as organism-environment interactions.